In the multiple-roll, extended-foil type capacitor, it is conventional to provide between the foil extensions at each end of each roll one or more electrical connections located at the end of the roll. It is also conventional to provide suitable electrical connections between the foil extensions of some of the adjacent rolls in the stack and, additionally, between the capacitor terminals and certain of the foil extensions at each end of the stack. Examples of extended-foil capacitors including such connections are shown in U.S. Pat. No. 4,633,369-Lapp et al and 4,467,397-Thiel et al.
The Lapp et al patent discloses the use of mechanical clips for making the connections between the foil extensions, the clips having teeth on their surfaces that penetrate the foil extensions when the clips are compressed about the edges of the foil extensions. This approach is subject to the disadvantage that these mechanical clips are relatively expensive and the additional disadvantage that the resultant joints do not provide metallurgical bonds between the foil extensions, which renders the joints more susceptible to impairment through surface oxidation.
The Thiel et al patent discloses the use of deposited metal along the edges of the foil extensions as part of a soldering process for connecting the foil extensions. A disadvantage of soldering is that it involves the use of heat and molten metal, which if not carefully controlled, can impair the closely-adjacent insulating film between the foil sheets. Furthermore, the foil, which is typically of aluminum, is difficult to join with solder because of the tenacious oxide coating that is typically present on aluminum, thus necessitating reliance upon expensive, labor-intensive soldering procedures, e.g., scrub soldering